Emission spectroscopic diagnostics of electron temperature distribution and electron number density distribution in the cathode region have been carried out employing an OMA/spectrometer system. Single color and two color pyrometry of cathode temperature distributions have also been performed. The experimental results are compared with results of a theoretical model formulated previously to study the are cathode interaction. The results show that the plasma in the cathode region strongly deviates from LTE. Thermionic cooling is the major cooling mechanism of cathodes at high are currents. The work function of 2% thoriated tungsten cathodes increases during arcing due to fast evaporation of thorium from 2% thoriated tungsten cathodes.N獲